Effect of polyvinylpyrrolidone on the catalytic properties of Pd/γ-Fe₂O₃ in phenylacetylene hydrogenation

Abstract

Maghemite nanoparticles modified with polyvinylpyrrolidone were synthesized using the chemical co-precipitation method. Palladium ions have then been immobilized on the PVP/γ-Fe₂O₃ magnetic support. The Pd-PVP/γ-Fe₂O₃ catalyst obtained was characterized using X-ray diffraction, thermogravimetry coupled with differential scanning calorimetry and quadrupole mass spectrometry, scanning electron microscopy combined with energy dispersive X-ray analysis, transmission electron microscopy, nitrogen adsorption–desorption and vibrating sample magnetometry. Morphology, microstructure, particle sizes and textural properties of the Pd-PVP/γ-Fe₂O₃ were compared with those of the unmodified Pd/γ-Fe₂O₃ catalyst, synthesized using the same method. The polymer has affected the size of γ-Fe₂O₃ nanoparticles and their agglomeration, forming compact microstructure with decreased mesopores (4.5 nm). Palladium nanoparticles with size of 3–5 nm were found both on the surface of the PVP/γ-Fe₂O₃ particles (6–10 nm) and inside the pores formed by them. The Pd-PVP/γ-Fe₂O₃ has demonstrated improved catalytic properties in phenylacetylene hydrogenation under mild conditions of 40 °C and 0.1 MPa, compared to Pd/γ-Fe₂O₃ and similar catalysts prepared using polyethylene glycol and pectin. The hydrogenation rate of C–C triple bond on Pd-PVP/γ-Fe₂O₃ achieved 2.8 × 10^–6 mol s⁻¹ and selectivity to styrene was 92%. The catalyst showed weak ferromagnetic and soft magnetic properties (M_S = 51 emu g⁻¹, M_r = 5.4 emu g⁻¹, and H_C = 71 Oe) and, therefore, can be easily recovered with an external magnet and reused for at least 11 runs without significant degradation in the catalytic activity.